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Heavy Metal Levels in Vegetables with Growth Stage and Plant Species Variations

Habib Mohammad Naser
Senior Scientific Officer
Soil Science Division, Bangladesh Agricultural Research Institute, Gazipur-1701.

Sarmin Sultana
Scientific Officer
Soil Science Division, BARI, Gazipur-1701,

Nashir Uddin Mahmud
Scientific Officer
Soil Science Division, BARI, Gazipur-1701.

Rebeca Gomes
Principal Scientific Officer
Soil Science Division, BARI, Gazipur-1701.

Shamsun Noor
Chief Scientific Officer & Head
Soil Science Division, BARI, Gazipur-1701.

Abstract/ Executive Summary:

Field experiment was conducted to compare and investigate the concentration levels of heavy metals in leafy vegetables with growth stage and plant species variations on an experimental field near the net house of Soil Science Division, Bangladesh Agricultural Research Institute, Joydebpur, Gazipur, Bangladesh during November 2008 to January 2009. Seeds of spinach (Spinacia oleracea), red amaranth ( Amaranthus tricolor) and amaranth ( Amaranthus oleraseus ) were sown on 14 November 2008. Plant and soil samples were collected at different growth stages, such as at 20, 30, 40, and 50 days after sowing (DAS). The concentrations of lead (Pb), cadmium (Cd), nickel (Ni), cobalt (Co), and chromium (Cr) in plant increased with the age of the plant, but the increase was not linear. The rate of increase of concentration of these metals at 20 to 30 DAS was found lower than that at 30 to 40 DAS, except Cr. Heavy metal content gradually increased at the early growing stage and fall during later stages of growth. The significant differences ( P < 0.01) were observed between the mean metal concentrations in the three vegetables species. The Pb and Co concentrations in amaranth were found higher compared to those found in spinach and red amaranth. Spinach exhibited higher levels of Cd and Cr than those of other vegetables. However, the three vegetables did not differ significantly in its Ni concentration. The order of heavy metal level in different vegetables was Cd

Keywords: Vegetables, Heavy metal, Concentration, Growth stage, Plant species

Location: Soil Science Division, Joydebpur, Gazipur, Bangladesh

Start Date: 00-11-2008

End Date: 00-01-2009

Program Area: Risk Management in Agriculture

Commodity: Amaranth

Objectives:

(i) To compare and investigate the concentration levels of heavy metals (Pb, Cd, Ni, Co, and Cr) at different growth stages of the commonly grown leafy vegetables;

(ii) To find out a growth stage, which stage is less content of heavy metals;

iii) To quantify the concentrations of heavy metal content by different vegetable species.

Methodology:

Experimental plots were set up on an experimental field near the net house of Soil Science Division, Joydebpur, Gazipur, Bangladesh during November 2008 to January 2009. The experimental field was top-dressed by foreign soil near about three years before. So, it is not represent the characteristics of Gazipur soils. Experimental plots consisted of three replicate rectangular areas (5 m × 2 m) for each leafy vegetable and each replicate was separated by 1 ft buffer area which was left as barren. Seeds of spinach ( Spinacia oleracea), red amaranth ( Amaranthus tricolor) and amaranth (Amaranthus oleraseus) were sown on 14 November 2008. Fertilizer s NPK were applied @ 75, 25, and 60 kg/ha from the source of Urea, triple super phosphate (TSP), and muriate of potash (MoP), respectively. Before fertilizer application and seeding initial soil sample (top soils, 0-15 cm) was collected. Initial soil an d fertilizers sample were analyzed in the laboratory. Plant and soil samples were collected at four growth stages of vegetables at 20, 30, 40, and 50 days after sowing. The samples were collected carefully using hand trowel to dig the soil around the plant and the plants were pulled out carefully, ensuring that no part of the root was lost. Plant samples were kept in separate polythene bags and properly labeled. Soil samples were collected at a depth of 0-15 cm from the same point of collecting plant samples. The samples were kept in polythene bags and labeled properly. The plant and soil samples were analyzed in the laboratory. The vegetable samples were washed in fresh running water to eliminate dust, dirt, possible parasites or their eggs and then again washed with deionized water. The clean vegetable samples were air-dried and placed in an electric oven at 65 °C for 72–96 h depending on the sample size. The dried vegetables samples were homogenized by grinding using a ceramic coated grinder used for metal analysis. All soil samples were spread on plastic trays and allowed to dry at ambient temperature for 8 days. The dried samples of soils were ground with a ceramic coated grinder and sieved through a nylon sieve. The final samples were kept in labeled polypropylene containers at ambient temperature before analysis. One gram of dry matter was weighed into 50-ml beaker, followed by the addition of 10 ml mixture of analytical grade acids HNO₃: HCIO₄ in the ratio 5:1. The digestion was performed at a temperature of about 190 ºC for 1.5 h. After cooling, the solution was made up to a final volume (30 ml) with distilled water in a volumetric flask. The metal (Pb, Cd, Ni, Co, and Cr) concentrations were determined by atomic absorption spectrometry using a VARIAN model AA2407 Atomic Absorption Spectrophotometer (AAS). Analysis of each sample was carried out three times to obtain representative results and the data reported in µg/g (on a dry matter basis). Statistical differences were performed by Tukey’s multiple comparisons test by using Excel Statistics version 4.0.

Source of Information: Bangladesh J. Agril. Res. 36(4): 563-574, December 2011

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Heavy metal content in different leafy vegetables varies significantly. The content varies with time of harvesting and stage of maturity of crops. The Cd and Cr contents in leafy vegetables in this study were detected higher while Pb and Ni were within the permissible limits as per the WHO standard but all the metals were within the maximum allowable level as per PFA, 1954, India. The magnitude of time dependence of plant metal concentration variations differed among crop species and metals. Further research is needed to obtain more specific information about the effect of age of the plants on accumulation and distribution of the heavy metal in the different plant parts, variations in uptake between different plant species, cropping history and fertilization.

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